An apparent mechanism dependence of radiated seismic energy
An apparent mechanism dependence of radiated seismic energy
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辐射地震能量的明显机制依赖性
DOI：
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发表时间：
2001
期刊：
影响因子：
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通讯作者：
G. Beroza
中科院分区：
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作者：
X. Pérez‐Campos;G. Beroza
我们发展了Boatwright和Choy[1986]确定辐射地震能量Es的方法的一个扩展，该方法考虑了偏差估计的因素。我们对1992-1999年期间全球204次地震应用我们的技术，发现走滑事件的视应力平均最大(0.70兆帕)，而反向和正常事件的视应力明显较小(分别为0.15和0.25兆帕)。这些结果支持Choy和Boatwright[1995]报道的ES的机制依赖性，尽管我们发现一旦解释了可能的偏差来源，机制依赖性就不像以前发现的那么强。机制依赖的来源尚不清楚，但一种可能性是，它反映了应力降中机制依赖的差异。这一假说是由走滑大地震中滑动宽度的标度提出的，并作了两个预测，可以用来检验它。首先，对于最大的倾滑地震，这种差异应该消失，因为断层的长度远远超过了向下倾斜的程度。第二点是，对于较小的地震，这种差异应该消失。第一个还无法测试，因为最近没有发生极大的倾角滑动地震。第二种观点得到了对较小地震对ES缺乏机制依赖性的支持。另一种假设是，如果断层在破裂过程中是不透明的，从而阻止穿过它们的地震辐射，可能会导致明显的机制依赖(Brune，1996)。这可能导致辐射的地震能量优先被捕获在倾斜断层的震源体积附近的地壳中。然而，从远震数据和区域数据获得的ES估计之间仍然存在很大的差异。这种差异表明对地震能量的远震和/或区域估计存在问题，必须在得出明确结论之前解决。
We develop an extension to the method of Boatwright and Choy [1986] for determining the radiated seismic energy Es that accounts for factors that bias the estimate. We apply our technique to 204 events worldwide during the period 1992–1999 and find that the apparent stress is on average largest for strike-slip events (0.70 MPa), while for reverse and normal events it is significantly smaller (0.15 and 0.25 MPa, respectively). These results support the mechanism dependence of Es reported by Choy and Boatwright [1995], although we find that once likely sources of bias are accounted for, the mechanism dependence is not as strong as found previously. The source of the mechanism dependence is unclear, but one possibility is that it reflects a mechanism-dependent difference in the stress drop. This hypothesis is suggested by the scaling of slip with width in large strike-slip earthquakes and makes two predictions, which could be used to test it. The first is that the discrepancy should disappear for the very largest dip-slip earthquakes as the length of the fault greatly exceeds the downdip extent. The second is that the discrepancy ought to disappear for smaller earthquakes. The first can not yet be tested due to a lack of recent, very large dip-slip earthquakes. The second is supported by the lack of mechanism dependence to Es for smaller earthquakes. An alternative hypothesis is that the apparent mechanism dependence could result if faults are opaque during rupture, blocking seismic radiation across them [Brune, 1996]. This could cause radiated seismic energy to be trapped preferentially in the crust near the source volume for dipping faults. There remains, however, a large discrepancy between estimates of Es obtained from teleseismic versus regional data. This discrepancy indicates a problem with teleseismic and/or regional estimates of the seismic energy and must be resolved before a definite conclusion can be drawn.